The objective of this research is to examine relationships among diet, blood and brain amino acid patterns and concentrations, brain neurotransmitter concentrations and amino acid metabolism, and feeding behavior. Changes in blood and brain amino acid and brain serotonin and catecholamine content of rats that have ingested diets differing greatly in protein content will be determined at intervals after ingestion of a meal. Effects of meals containing additions of amino acids that are elevated in brain or blood will be tested for their ability to influence the amount of protein consumed by rats subsequently offered the choice of two diets differing in protein content. Mini-pumps will be used to infuse directly into the brain amino acids that influence food intake or preference in order to determine whether or not effects on feeding behavior can be reproduced by infusions into specific areas of the brain. Rats with lesions in brain areas known to be associated with control of food or amino acid intake will be used to determine whether some such lesions will eliminate the response to dietary additions or infusions of amin acids that alter food intake or preference. Such measurements will be made on rats that have eaten diets containing increased amounts of amino acids that compete for uptake into brain with the amino acid that is limiting for growth; atypical, non-protein amino acids will also be used. Lesioning and infusion methods will be used to determine if the reduced food intake caused by dietary GABA may be due to peripheral effects or possibly to direct effects on the CNS. Effects of alterations in the brain amino acid pool (by either dietary imbalances of amino acids or changes in total protein intake) on the integrity of protein-synthesizing systems (polysomes) and on protein synthesis and turnover will be examined with in vitro and in vivo systems. These studies can contribute information important in treatment of various conditions such as liver disease, genetic defects, and behavioral disorders such as obesity and anorexia nervosa.